From DE 197 49 074 A1 an agricultural utility vehicle with a mechanical-electrical torque division gearbox is known. Here an internal combustion engine is connected with a first gearbox interface of a combination gearbox and an electrical machine is connected with a further gearbox interface of the combination gearbox. The combination gearbox is used for the forward propulsion drive of the utility vehicle. A generator driven by the engine drive shaft is provided, that supplies the electrical machine with electrical power. Thereby a mechanical-electrical torque division can be achieved, that makes possible an infinitely variable forward propulsion drive of the utility vehicle, where a higher efficiency can be attained in contrast to a conventional torque division gearbox configured as a hydrostatic drive. On the other hand the power take-off shaft is connected to the internal combustion engine over a purely mechanical gearbox, so that the power take-off shaft rotational speed is in a fixed relationship to the rotational speed of the internal combustion engine.
Operating implements can be adapted to an agricultural utility vehicle, for example, to a tractor, that must be driven mechanically over a power take-off shaft of the utility vehicle. Such an operating implement is, for example, a non-self propelled rotobaler. In the sense of the present invention the drive interface is understood to mean an attached implement driven by the vehicle, that makes a mechanical torque available.
When operating implements that must be operated at a constant input rotational speed, are adapted to a vehicle with a power take-off shaft according to DE 197 49 074 A1, the internal combustion engine must be operated at a constant rotational speed for trouble-free operation of the operating implement, since the power take-off shaft is in a fixed rotational speed relationship to the rotational speed of the internal combustion engine. Thereby an infinitely variable gearbox must be provided in the drive-line of the main propulsion drive, in case that a change in the propulsion speed of the vehicle is to be performed. This is expensive and costly since this requires an infinitely variable power shift gearbox.
In case that operating implements are to be attached to a vehicle which must be operated at a power take-off shaft speed proportional to the forward propulsion velocity of the vehicle, a trouble free operation is only possible if the rotational speed of the internal combustion engine is actually proportional to the forward propulsion velocity. If the wheels of the vehicle spin, for example, on a tractor in the field, the forward propulsion velocity of the vehicle is reduced. In case the power take-off shaft speed remains unchanged, the proportionality of the power take-off shaft speed to the forward propulsion velocity is changed and the rotational speed of the operating implement will increase relative to the forward propulsion velocity. In sowing machines this can have the effect that the plants are planted at irregular intervals.
The task underlying the invention is seen in the need to define a drive arrangement for attached implements for a vehicle of the aforementioned type through which the above problems are overcome. In particular a constant power take-off shaft rotational speed should be made available despite a varying rotational speed of the internal combustion engine. Furthermore with a generally constant internal combustion engine rotational speed a variable power take-off shaft rotational speed should be generated.